Methods of production of novel molybdenum-sulfide dimers and reactions of the same

ABSTRACT

Derivatized molybdenum-sulfide dimers of the general formula [(C 5  R 5  Mo) 2  (μ-S) 4-x  (μ-SR) x  ] n  are utilized in the solid state, incorporated in permselective membranes and in aqueous solution as chemical specific complexing agents in various separation processes.

This is a divisional of application Ser. No. 07/750,045, filed on Aug.27, 1991, now U.S. Pat. No. 5,391,791.

FIELD OF THE INVENTION

This invention describes a variety of novel molybdenum-sulfide dimercompounds. These dimer compounds are characterized by their ability toreversibly bind alkenes and/or their ability to react with alkynes.Based on various alterations of the basic molybdenum-sulfide dimerstructure, the dimers of the present invention exhibit varying usefulproperties such as water solubility and ligand reactivity. Also includedin this invention are processes that use the molybdenumsulfide dimercompounds in olefin separation and acetylene removal processes.

BACKGROUND OF THE INVENTION

In a series of related papers, M. Rakowski DuBois and co-workers havedescribed the existence of a novel class of molybdenum-sulfide dimercompounds. See, e.g., M. Rakowski DuBois et al., J. Am. Chem. Soc., vol.101, pp. 5245-5252 (1979); M. Rakowski Dubois et. al., Inorg. Chem.,vol. 20, pp. 3064-3071 (1981); M. McKenna et al., J. Am. Chem. Soc.,vol. 105, pp. 5329-5337 (1983); and J. Birnbaum et al., Organometallics,vol. 10, pp. 1779-1786 (1991). The dinuclear sulfide bridged molybdenumdimers have the general formula [(C₅ H₅ Mo)₂ (μ-S)_(4-x) (μ-SR)_(x)]^(n), where x=0-3, and n=0, +1, -1.

Surprisingly, it has been shown that these molybdenum-sulfide dimerswill undergo reversible interactions with olefins. Of course, thereversible interactions of olefins with a variety of transition metalions has been known for many years. For example, Ag(I) binds reversiblywith olefins. However, the reactions of these dimers with olefins isfundamentally different from those characterized for silver and othermetal ions because it is the sulfide ligands of the molybdenum-sulfidedimers that act as the site of olefin binding. A typical reaction isshown below. ##STR1##

A series of experiments were performed to determine the equilibriumconstants for the above reaction in chloroform for a series of olefins.See, McKenna Supra. The data indicate that some of the binding constantsare in the same range as those observed for olefin binding to the silverion. It was also shown that the equilibrium constants were quitesensitive to the steric and electronic features of the olefin. Forexample, the equilibrium constant for trans-2-butene at 26° C. was foundto be (3±1)×10² while cis-2-butene was 17±2 and cis-2-hexene was3.9±0.2.

In addition to its reactivity to olefins, the molybdenum-sulfide dimersof Rakowski Dubois have also been shown to form irreversible adductswith acetylene to yield thermally stable alkenedithiolate compounds asshown in a typical example below. ##STR2##

Although the alkenedithiolates formed are considerably more stable thanthe molybdenum-sulfide olefin adducts, they are not unreactive. See,McKenna supra. For example, exchange reactions between certainalkenedithiolates and various alkynes have been detected. It has alsobeen shown that the alkenedithiolates can be hydrogenated under mildconditions to yield the original molybdenum-sulfide dimer and thecis-alkene as shown below: ##STR3## Under the mild reducing conditionsemployed, the alkanedithiolate moiety of the dimer (in the example, themethylene dithiolate) is not reduced.

In a few instances, the ability of metal ions to bind reversibly toolefins has been utilized in olefin separation and purification systems.For example, olefin adducts of Ag(I) ion have been used inchromatographic systems for the separation of olefins. More recently,aqueous silver nitrate solutions have been used to separate ethylene orpropylene from purified multicomponent gas streams. See, U.S. Pat. No.4,174,353 of Marcinkowsky et al. A major concern when utilizing thesilver/olefin adduct chemistry, is that the silver ion forms a complexwith acetylene which is explosive when dry and rigorous methods must beemployed to remove acetylene from any gas stream that will come incontact with the silver ion. A further problem associated withsilver/olefin separation schemes, is that the silver ion is rapidlypoisoned by H₂ S, a common impurity in gas associated with the thermalcracking of hydrocarbons.

In contrast to the use of metal ion chemistry in olefin separationschemes, the molybdenum-sulfide dimers are unaffected by the presence ofH₂ S. In addition, the inventors of the present invention have alsodescribed how the ability of the molybdenum-sulfide dimers to bind andto subsequently reduce alkynes may be used in alkyne removal processes.

Prior to the conception of this invention, molybdenum-sulfide dimers hadnot been developed for use in any way other than as an interesting andunique chemical compound. For example, the molybdenum-sulfide dimersreported to date have not been water soluble, and the olefin alkeneadduct reactions have only been studied in chloroform or other organicsolvents.

One of the primary features of the present invention is the separationor purification of olefin streams. Olefins are generally produced viacatalytic cracking processes. Such processes produce refinery-gradeolefins (65-70% purity). Currently, refinery grade olefins are furtherseparated and purified using distillation columns to producepolymer-grade olefins (99.5% purity) or chemical-grade olefins (95%purity). Frequently two distillation columns must be employed. Eachdistillation step is expensive and energy intensive, and evenincremental gains in purity greatly increase the costs of the olefinproducts.

Current theories for improving the economies of olefin separations andpurifications suggest that a hybrid separation process be utilized. Inaddition to the conventional distillation step, some other chemicallyspecific process would be utilized to enhance olefin purity for greatlyreduced costs. Processes that have been suggested as potentially beingamenable to the hybrid approach are the following: 1) a facilitatedtransport membrane using a chemically-specific complexing agent; 2)absorption/stripping with a chemical solvent; and 3)adsorption/desorption on a solid support.

The rationale for the use of hybrid olefin separation processes is asfollows: conventional separation technology can only achieve a certainlevel of separation per stage. This level of separation is not aconstant for each stage. As higher purity levels are required, thenumber of stages increases rapidly. This also means a dramatic increasein the costs for additional processing equipment. On the other hand, aseparation step using reversible chemical complexation obtains improvedselectivity at the same time that the driving force of conventionalolefin separation processes decreases. Although this is not intuitive,it occurs because there is a large excess of complexing agent presentand the selective reaction becomes very efficient. The hybrid process,therefore, typically combines a conventional separation process toachieve a certain level of purity and follows it with a separation stepusing reversible chemical complexation to "polish" or further purify thedesired product. See, Haggin, Chem. & Eng. News., pg. 23-24 Feb. 25,1991.

The present inventors have recognized the potential themolybdenum-sulfide dimers have as part of a hybrid olefin separationprocess. Previous reversible binding systems have used AgNO₃ or coppercompounds as complexing agents. As described above, AgNO₃ reactsirreversibly with sulfur compounds. Copper compounds are verysusceptible to reactions with oxygen, water or sulfur compounds. Suchreactions lead to very poor lifetimes in operation or, in thealternative, lead to the higher costs required for removing thecompounds prior to separation and purification. Similar problems existwith acetylene (when purifying ethylene) and propyne (when purifyingpropylene). Again, the alkyne impurities increase costs either bygreatly reducing the lifetime of the complexing agent, or by themechanism required to remove the alkyne prior to the separating processutilizing the complexing agent.

Acetylene removal typically may be accomplished in a variety of manners.In one process, the gaseous feed stream is passed through a chilledpolar solvent such as dimethyl formamide (DMF). A pressure swing is thenused to recover the acetylene. Another method is the dehydrogenation ofthe acetylene over a noble metal catalyst.

The present invention describes .modified molybdenum-sulfide dimershaving characteristics that will allow this unique family of compoundsto be used in a variety of processes, including alkeneseparation/purification processes.

SUMMARY OF THE INVENTION

The present invention includes, most fundamentally, the utilization of aclass of molybdenum-sulfide dimer compounds in olefinseparation/purification processes and for the complexation andsubsequent reduction of alkynes.

Included herein are molybdenum-sulfide dimer compounds of the generalformula [(C₅ R₅ Mo)₂ (μ-S)_(4-x) (μ-SR)_(x) ]^(n) where x=0-3, and n=0,+1, -1, that are modified to be used in commercially viable processes.Modifications of the dimers include chemical modifications such as thesynthesis of water soluble dimers and dimers containing functionallyreactive ligands that can be used to incorporate the dimer within thematrix of polymeric materials. Modifications also include supporting themolybdenum-sulfide dimer on solid supports. In one embodiment of theinvention, the dimer is supported in an ion-exchange membrane.

Due to the novel formulations/modifications of the molybdenum-sulfidedimers, the reversible complexation with olefins and the irreversiblecomplexation with alkynes have been shown to be functional in theaqueous phase, in solid state reactions, and within a membrane matrix.

The advantages of having olefin complexing agents in aqueous solutionhave to do with the fact that olefins have a much lower solubility inwater than in organic solvents. The total amount of olefin in solutionis based on physical solubility--which is usually a poor separationcriteria--and the quantity of olefin bound to the complexing agent.Reducing the physical solubility increases the chemical specifity of thesolution, and therefore, the selectivity of the separation process.

The complexing agents in solution can be used in either a directgas-liquid contactor or a membrane separation device. Gas-liquidcontacting can be accomplished via packed columns, open columns or byvarious staging approaches. In a membrane separation device, separatephases are maintained on opposite sides of a permselective membrane.Mass flow of the olefin in the first solution occurs across the membraneand the second solution is enriched in the olefin that is selected forby the complexing agent incorporated into the membrane.

In another embodiment using membrane separations, the membrane may serveas a permselective barrier between feed or receiving phases and thesolution contains the complexing agent. The solution may or may not"wet" the membrane and enter the pores of the membrane. This embodimentis normally termed a membrane contactor.

Gas phase/solid phase separations can be performed when utilizing thesupported molybdenum-sulfide dimers of the present invention. Suchseparations will generally be accomplished on a column.

The separations that are included within the scope of this invention byuse of the molybdenum-sulfide dimers include the separation of olefinsfrom alkanes (e.g., ethylene from ethane, propylene from propane), theseparation of alkenes (e.g., ethylene from propylene), the separation ofolefin isomers (e.g., cis-2-butene from trans-2-butene), the separationof olefins from alkynes (e.g., propylene from propyne) and the removalof acetylene from a gaseous hydrocarbon feed stream. In a furtherembodiment of the invention, the molybdenumsulfide dimers are"catalytic" in the reduction of alkynes.

The various aspects of the invention are described in more detail below.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention describes the use of a unique class of inorganiccompounds in olefin separation/purification processes and for alkyneremoval or reduction processes. The unique class of inorganic compoundsis defined by their ability to reversibly bind olefins and to moretightly bind alkynes. In the preferred embodiments of the invention, theinorganic compounds are molybdenum-sulfide dimer compounds of thefollowing general formula: [(C₅ R₅ Mo)₂ (μ-S)_(4-x) (μ-SR)_(x) ]^(n),where x=0-3, and n=0, +1, -1. This core structure can be depicted asfollows for x=2 and n=0: ##STR4##

In various embodiments of the invention, this core molybdenum-sulfidedimer structure can be modified in a limited number of ways.Substitutions can be made to the alkanedithiolate moiety R or to thecyclopentadienyl moieties Cp.

The various derivatives--many of which are water soluble or may beeasily made water soluble--of the molybdenum-sulfide dimer retain theirability to reversibly bind alkenes and to form alkenedithiolatecompounds upon reaction with alkynes. As discussed below, theseproperties, in conjunction with their water soluble properties, enablesthe use of such materials in various alkene separation/purificationprocesses.

In an additional embodiment of the present invention, it is desired thatthe molybdenum-sulfur dimer be a polymer precursor. In one preferredembodiment of the molecule having this type of functionality Cp=C₅ H₄CHCH₂. Various specific embodiments of the modified molybdenum-sulfidedimers of the present invention are given in TABLE 1.

                  TABLE 1                                                         ______________________________________                                        R            C.sub.p         Property                                         ______________________________________                                        --CH--CO.sub.2 Na                                                                          C.sub.5 H.sub.5 water solubility                                 --CHC(CH.sub.3).sub.2 CO.sub.2 Et                                                          C.sub.5 H.sub.5 water solubility                                 --CHC(CH.sub.3).sub.2 CO.sub.2 Li                                                          C.sub.5 H.sub.5 water solubility                                 --CHCH(CO.sub.2 CH.sub.3).sub.2                                                            C.sub.5 H.sub.5 water solubility                                 --CH.sub.2   C.sub.5 H.sub.4 CO.sub.2 CH.sub.3                                                             water solubility                                 --CH.sub.2   C.sub.5 H.sub.4 CO.sub.2 Na                                                                   water solubility                                 --CH.sub.2   C.sub.5 H.sub.4 CONH(CH.sub.2).sub.x                                                          water solubility                                              NHR.sub.2.sup.+                                                  --CH.sub.2   C.sub.5 H.sub.4 CHCH.sub.2                                                                    prepolymer                                       ______________________________________                                    

Additional embodiments of the derivitized molybdenum-sulfide dimers ofthe present invention have the general structure: ##STR5## In one suchembodiment, R'=CH(CH₃)CO₂ H. Such derivatives are also more soluble inwater than the base dimer.

The present invention is not, however, limited to the modified membersof the molybdenum-sulfide dimer family listed in Table 1. Compounds thatare homologous to the listed dimers, specifically those that can beprepared generally according to the procedures as described in Examples1 and 2 below, are included within the scope of this invention.

Water soluble molybdenum-sulfide dimer, therefore, is hereby defined toinclude all compounds containing molybdenum and sulfur capable offorming chemically- or thermally-reversible alkanedithiolate oralkenedithiolate complexes that have significant solubility in water oraqueous solvents.

The water soluble molybdenum-sulfide dimers of the present inventionhave been shown to form complexes with olefins. The equilibrium constantfor the following reaction has been determined. ##STR6## For the abovereaction the equilibrium constants for R=H, R'=CH₃ K=4200 and forR=R'=CH₃ K=245. Experimental details of these experiments are set forthin Example 3 below.

Additional equilibrium constants for a wide variety of water solublemolybdenum-sulfide dimers are shown in Table II below. For certaincases, the olefin complexation reactions were carried out in eitheraqueous or non-aqueous solutions in the presence of about one equivalentof H2S per equivalent of dimer. No inhibition of the olefin binding isdetected in the presence of H₂ S.

                  TABLE II                                                        ______________________________________                                                                       K.sub.eq at                                                                   25° C.                                  Complex (Solvent)    Olefin    (M.sup.-1)                                     ______________________________________                                         ##STR7##            Ethene Propene t-2-Butene c-2-Butene c-2-Hexene                               Styrene c-Stilbene                                                                      >10.sup.4  >10.sup.4  1.4 × 10.sup.3                                     17 4 90 <1                                     ##STR8##            Ethene Allene Propene 1-Butene c-2-Butene t-2-Butene                          sobutene Styrene                                                                        >10.sup.4  > 10.sup.4  1200 460 20 450 5                                      10                                              ##STR9##            Ethene    150                                             ##STR10##           Ethene Propene 1-Butene t-2-Butene Styrene                                              42,200 1,500 600 220 20                         ##STR11##           Ethene Propene t-2-Butene Styrene                                                       10.sup.4  4,200 245 60                          ##STR12##           Ethene Propene                                                                          95 5                                           ______________________________________                                    

In Example 5, procedures are described for demonstrating theeffectiveness of molybdenum-sulfide dimers, specifically water solublemolybdenum-sulfide dimers, as olefin transport agents in an aqueousliquid membrane. The molybdenum-sulfide dimers of the present inventionmay be utilized in a variety of separation processes in order to achievethe variety of useful chemical separations to which they may be capableof performing. The separation processes include liquid/liquid,gas/liquid, liquid/solid and gas/solid procedures that are familiar tothose skilled in the art.

As described above, chemically-specific agents incorporated intomembranes can be used in olefin separation/purification processes. (Bymembrane transport action, the complexed olefin will migrate within, andbe released on, the other side of the membrane.) In one non-limitingembodiment of the present invention, a molybdenum-sulfide dimer of theinvention is made part of a membrane. Preferably, the dimer is a watersoluble molybdenum-sulfide dimer, and the membrane is an aqueous liquidmembrane. This method can also be used with a cast polymer film.

The membrane contactor can be used in a variety of ways to affect-alkenepurification/separation. In a non-limiting example, a feed gas streamcontaining relatively high purity propylene, contaminated with propane(and/or high molecular weight alkenes) is introduced into one side ofthe membrane contactor. The liquid stream on the opposite side of themembrane will be enriched in propylene relative to the feed stream. Thisis due to the relative specificity of the dimer to complex with thepropylene in preference to the other components of the feed stream.

In another embodiment of the present invention, feed gas streamscontaining mixtures of olefins, e.g., cis and trans 2-butene, may beseparated by the ability of the membrane supported molybdenum-sulfidedimer to preferentially bind and transport trans-2-butene.

The present invention also includes the membranes supporting themolybdenum-sulfide dimers. In one embodiment of the present invention,and as described in Example 5 below, cationic molybdenum-sulfur dimersare incorporated into ion exchange membranes. In a preferred embodiment,ion exchange membranes referred to as NAFION ion exchange membranes(NAFION is a registered trademark of E. I. du Pont Ne Mours & Co.) ofvarying thickness are used to support the molybdenum-sulfide dimers. Upto 80% of the available ion exchange sites within the ion exchangemembranes may incorporate molybdenum-sulfide dimers of the presentinvention. In preferred embodiments, the ion exchange membranes areloaded to between 10 and 80% of capacity with the molybdenumsulfidedimer [C₅ H₅ Mo)₂ (S₂ CH₂)(μ-S)(μ-SCMe₃)]⁺. In an alternate embodiment,anionic molybdenum-sulfur dimer ##STR13## may be loaded onto an anionicion exchange membrane, for example RAIPORE anion exchange membrane.(RAIPORE is a registered trademark of The Electrosynthesis Co.)

The modified monomer (or prepolymer) derivatives of themolybdenum-sulfide dimers of the present invention are designed for theproduction of polymeric forms of the molybdenum-sulfide dimers or ofpolymeric materials that are covalently linked to the molybdenum-sulfidedimers. Polymers may be produced from the vinyl containing dimers byprocesses well known to those of ordinary skill in the art. The monomerunits may be used alone or with copolymers. The term prepolymer, as usedherein, is to be interpreted to also include block co-polymers and asagents attached as a side chain on a polymer backbone.

In an additional embodiment of the present invention, it has been shownthat the molybdenum-sulfide dimers will also react in the solid statewith alkenes and alkynes. The solid state dimer, in either granular orpowder forms, or as a thin film will react reversibly with alkenes andirreversibly with alkynes in much the same manner as in solution. Thisunanticipated result demonstrates that gas/solid separation/purificationschemes may be performed utilizing the molybdenum-sulfide dimers of thepresent invention.

In one embodiment of the present invention, solid state films of themolybdenum-sulfide dimers are deposited on the surface of supportmaterials and the supported solid state materials used in either batchor flow gas separation processes. In one embodiment, a solid supportedmolybdenum-sulfide dimer is contained in a column and used to removealkynes from stream gases. After the dimer material has reachedsaturation by reaction with alkynes to form alkenedithiolate complexes,the unit holding the complexes can be treated by flowing H₂ at aslightly elevated temperature to release alkenes and return themolybdenum-sulfide dimer supported material to an active form to be usedfor further alkyne removal.

In a preferred embodiment of the invention, the support material iscommercially available neutral alumina. The molybdenum-sulfide dimer maybe placed on the aluminum support according to the procedures describedin Example 6 below. Commercially available silica supports may also beutilized for this purpose.

According to the present invention, the molybdenum-sulfide dimers insolution may be used in a direct gas-liquid contactor or a membranecontactor. Under certain operating regimes and for certain separations,liquid/liquid contacting may also be utilized. There are a variety ofmethods for gas-liquid contacting; e.g., packed columns, open columns,and various staging approaches. As discussed above, a membrane contactoris a device in which the liquid phase is passed on one side of amembrane and the olefin phase is passed on the opposite side of themembrane. Mass transfer takes place across the membrane.

In a preferred embodiment of the invention, the molybdenum-sulfidedimers--in solid state, membrane supported or membrane incorporatedforms--can be utilized in at least two areas in the conventional processutilized to produce ethylene and propylene from ethane and propane. Thedimers may be used to replace the current alkyne removal module, andalso as a chemically specific portion of a hybrid separation process foralkene separation or purification.

The following Examples, along with the skill and knowledge possessed byone of ordinary skill in the art, provides specific illustrations of thevarious aspects of the present invention.

EXAMPLE I SYNTHESES OF IONIC WATER SOLUBLE MOLYBDENUM SULFIDE DIMERSWITH OLEFIN BINDING CAPABILITIES

The base or core structure of the molybdenum sulfide dimers may bemodified by the introduction of substituents on the cyclopentadienyl oralkanedithiolate ligand positions. In one embodiment of the invention,the alkanedithiolate position may be altered according to the followingreaction: ##STR14## The dihydro-molybdenum sulfide dimer startingmaterial was made according to the procedures described in RakowskiDuBois et al. J. Am. Chem. Soc., vol. 102, pg. 7456 (1980). Reactionwith the sodium or potassium salt of dibromoacetate and a base,preferably sodium methoxide, in tetrahydrofuran solvent at 25° C. forone hour led to the formation of the water soluble product 1. Thereaction and resulting product must be protected from air. Following thereaction, solvent was removed and the product 1 was extracted withmethanol and filtered through celite. Upon reduction of solvent, theproduct was obtained as a crystalline solid.

The structure of 1 is confirmed by proton NMR spectroscopy: ¹ H NMR (ppmin D₂ O): 6.51, 6.39 (2s, Cp); 3.39 (s, CH). It has been shown that 1reversibly binds with alkenes in water or alcohol solutions.

Derivatives of the molybdenum-sulfide dimers with water solublesubstituents on the alkanedithiolate moiety were also prepared accordingto the following formula: ##STR15## where MR═NaCH (CO₂ CH₃)₂. In otherembodiments, MR may be LiC(CH₃)₂ CO₂ Et or LiC(CH₃)₂ CO₂ Li. Thestarting material for this reaction 2, is prepared according to theprocedures described in Birnbaum et al. Organometallics, vol. 9 pg. 156(1990). Reaction with the nucleophiles occur at ambient temperatures inan organic solvent such as THF. Esters in the final products 3, may behydrolyzed by conventional means to increase water solubility of thefinal products.

Further substitution of sulfide ligands in these structures can beaccomplished with alkyl halides or acids, as shown below: ##STR16## Insome cases these cations retain the ability to interact reversibly witholefins.

A second class of water soluble molybdenumsulfide dimers consists ofcompounds where the cyclopentadienyl moieties have been modified. Aprocedure for synthesizing [(C₅ H₄ CO₂ Me)MoSC₂ H₄ S]_(z) is asdescribed below: ##STR17## The esterified cyclopentadiene C₅ H₄ CO₂ Meis prepared according to the procedures described in Macomber et al.Adv. in Organomet. Chem., vol. 21, pg. 1 (1982). This material isreacted with molybdenum carbonyl and sulfur, and then with ethylene.Reaction conditions are equivalent to those described for the synthesisof the homologous product with unsubstituted Cp ligands. See, RakowskiDuBois et al., Inorg. Chem., vol. 20, pg. 3064 (1981). The estersubstituted product 4 of this reaction was then hydrolyzed under basicconditions to produce the water soluble product 5 with carboxylatesubstituents as seen below: ##STR18## This water soluble product 5 hasbeen characterized by NMR spectroscopy. ¹ H NMR (ppm in D₂ O): 5.0, 5.2(2 trip. Cp); 1.7 (s, C₂ H₄). Dimer 5 may be thermally activated torelease ethene under an active vacuum to form the water soluble dimer 6.##STR19## The water soluble molybdenum-sulfide dimer 6 may reactreversibly with alkenes or form more stable adducts with alkynesaccording to the teachings of this invention.

The dimers 5 or 6 may also be used to prepare cationic derivatives byconverting the ester substituent to amino substituted amides 7 byconventional organic amide synthesis; as would be familiar to those ofordinary skill in the art, as follows: ##STR20##

EXAMPLE 2 SYNTHESIS OF POLYMER PRECURSOR MOLYBDENUM-SULFIDE DIMERS WITHALKENE BINDING CAPABILITIES

The introduction of an aldehyde substituent into the cyclopentadienylligand of the molybdenum-sulfide dimers of the present invention wasaccomplished as follows: ##STR21## The free aldehyde cydopentadienylligand 8 was prepared as described in Macomber et al. supra. Thereaction to form the aldehyde substituted molybdenum-sulfide dimer 10was then performed generally according to the procedures for synthesisof the unsubstituted molybdenum dimer as described in McKenna et al.supra and Rakowski DuBois et al. (1981) supra.

The propane dithiolate dimer 9 dissociates propene at 50° C. In thepresence of excess ethylene, the thermal activation of 9 leads to theformation of dimer 10. Dimer 10 was isolated by chromatography of thethermal activation product mixture through an alumina column with asolution of 50:50 by volume CH₃ CN/CH₂ Cl₂. A first brown fraction wasisolated by solvent removal and characterized as dimer 10 by NMRspectroscopy. ¹ H NMR (ppm in CDCl₃): 5.35 (s, Cp), 9.29 (s, CHO); 1.90(s, C2 H₄). A second fraction eluted from the column was shown to be themono-aldehyde 11. ##STR22## Dimer 11 was also characterized by NMRspectroscopy. ¹ H NMR (DCCl₃): 5.28, 5.26 (2 trp. Cp CHO); 5.10 (s, Cp);9.25 (s, CHO); 1.8, 1.9 (m, C₂ H₄).

The aldehyde substituted molybdenum-sulfide dimers 10, 11, may bereacted with methylenetriphenylphosphorane to lead to the formation ofvinyl substituted dimers, as shown below. ##STR23## The vinyl formingreaction may be performed generally according to the proceduresdescribed for other aldehyde Cp systems, see for example Rausch et al.,J. Organametallic Chem., vol. 205, pg. 353 (1981). The vinyl derivativesmay then be converted into polymeric materials as a co-polymer ormonomer unit by redox or other well known polymerization formationprocesses. The polymeric molybdenum-sulfide dimer compounds may be usedin the solid state separately or as supported materials, or may be usedin membrane synthesis to form membrane materials containing themolybdenum-sulfide dimer functionality.

EXAMPLE 3 OLEFIN INTERACTIONS WITH MOLYBDENUM-SULFIDE DIMERS AND OLEFINSEPARATIONS

Equilibrium constants for the following reaction were determined by NMRspectroscopy. ##STR24## A small excess of olefin was added to an aqueous(D₂ O) solution of 1 of known concentration in an NMR tube, and the tubeflame sealed. NMR integrations were determined for resonancescorresponding to each compound in solution at periodic intervals (over0.5 to 5 days) until relative concentrations of 1 and 13 remainedconstant. Equilibrium ratios were calculated using the integrationratios and the known initial concentration of dimer 1.

Equilibrium constants for an extensive series of molybdenum-sulfidedimers can be seen in Table II. For selected cases, the olefincomplexation reactions were carried out in either aqueous or non-aqueoussolutions in the presence of at least about one equivalent of H₂ S perequivalent of molybdenum-sulfide dimer. No inhibition of the interactionwith olefins was detected in the presence of the H₂ S.

To demonstrate the principle of alkene separations using themolybdenum-sulfide dimers as olefin transport agents in an aqueousliquid membrane, a simple experimental apparatus 18, such as depicted inFIG. 1, may be used. An olefin mixture may be dissolved in an organicsolvent in section 20. Aqueous solution containing themolybdenum-sulfide dimer is held in the middle lower section of theapparatus 22, and is stirred mechanically. Organic solvent is also foundin section 24 of the apparatus. The concentration gradient of olefin inorganic solvent 24 can then be monitored periodically by gas liquidchromatography.

In reactions of dimers with olefin mixtures, selective complexation ofthe less sterically hindered olefin by the molybdenum-sulfide dimer isfavored as shown in the equilibrium constant studies. Rates of olefincomplexation to the sulfide ligands are known to be rapid. See DuBois etal. J. Am. Chem. Soc. vol. 103, pg. 3429 (1981). These experiments willindicate the rates of olefin dissociation.

EXAMPLE 4 INTERACTIONS OF MOLYBDENUM-SULFIDE DIMERS WITH ALKYNES

A number of the modified molybdenum-sulfide dimers of the presentinvention were shown to undergo reactions with alkynes in a manneranalogous to that shown for the unmodified dimers. See, McKenna et al.supra; Rakowski DuBois et al. supra. For example, dimer: ##STR25## inCD₃ OD in the presence of three equivalents of acetylene at roomtemperature reacted almost immediately to form the alkenedithiolate. Thealkenedithiolate product (MeCpMo)₂ (S₂ CHCO₂ ⁻)(SC₂ H₂ S) was identifiedby NMR spectroscopy. ¹ H NMR: (CD₃ OD): 6.86 (s,S₂ CHCO₂ ⁻); 6.56 (s,S₂C₂ H₂); 5.69, 5.60 (m, Cp); 2.09, 1.98 (2s, MeCp).

In a similar experiment the diethanedithiolate modified dimer ##STR26##was reacted with excess phenyl acetylene in CHCl₃ as shown below:##STR27## Again, the product was identified by NMR spectroscopy inCDCl₃. ¹ H NMR: 7.2 (m,Ph); 6.65 (s, C═CH); 6.15, 5.9 (2t, Cp); 3.15 (s,OMe).

A modified alkene dithiolate dimer was reacted with hydrogen at 25° C.as shown below. ##STR28## This reaction, with the H₂ at a pressure of150 mm, was substantially completed in three days. The analogousreaction using the alkenedithiolate with both Cp groups containingesters took 23 days to reach completion. The reduction step of themolybdenum-sulfide dimer alkyne adduct to yield the dimer used to "trap"the alkyne is important in providing a reusable system for alkyneremoval.

EXAMPLE 5 MEMBRANE SUPPORTED COMPLEXES

Cationic molybdenum complexes were incorporated into NAFION ion exchangemembranes of varying degrees of thickness. For example, when a sample ofNAFION (25 μM thickness) is soaked in a 10⁻² M methanol solution of [(C₅H₅ Mo)₂ (S₂ CH₂)(μ-S)(μ-SCMe₃)]⁺ 15, for 15-30 min., the membrane takeson the purple color of the cationic complex. The amount of 15incorporated into the NAFION membrane was determined by measuring thechange in concentration of 15 in the methanol solution (by visibleabsorption spectrometry) and by measuring the mass change of themembrane resulting from the ion exchange process. (Calculations fromboth methods indicated that 45% of the sodium ions in the originalmembrane had exchanged with the molybdenum cation.) Similar experimentswere carried out with other thicknesses of ion exchange membrane andwith other cationic complexes of the formula [(CpMo)₂ (S₂CH₂)(μ-S)(μ-SR)]⁺.

    ______________________________________                                        R             Nafion Thickness                                                                           % Loading                                          ______________________________________                                        CMe.sub.3     25 uM        45                                                 CMe.sub.3     175 uM       35                                                 CH(Me)CO.sub.2 H                                                                            25 uM        41                                                 ______________________________________                                    

In a similar procedure, the anionic complex 1 has been exchanged into aRaipore anion exchange membrane. The manipulations of 1 and itssubstituted membrane however must be carried out in an air-freeenvironment.

In CH₂ Cl₂ solution, 15 interacts reversibly with ethene with a K_(eq)=95 at 20° C. as shown below: ##STR29## K_(eq) for the interaction of 15with propene is 5 at 20° C. The complex does not react with alkanes. Onthe basis of this behavior of the cation in solution, it is seen thatthe cation-substituted membrane will function as an efficient device forseparating ethene from propene, and for separating ethene from saturatedhydrocarbons.

EXAMPLE 6 Reactions of Molybdenum Complexes in the Solid State withAlkenes and Alkynes

A solid sample of (C_(p) Moμ-S)₂ S₂ CH₂ was found to react reversiblywith olefins. For example, when two equivalents of ethene were added toa solid sample of the molybdenum complex at room temperature, a gradualcolor change to brown was observed. After three days, the unreactedethene was removed and the solid was dissolved in CDCl₃. The ¹ H NMRspectrum of this sample showed that ca. 75% of the solid had beenconverted to the ethanedithiolate complex. The solvent was removed fromthe sample and the solid material was heated at 50° C. under vacuum fortwo days. The NMR spectrum of the resulting product indicated that 82%of (CpMoμ-S)₂ S₂ CH₂ had been reformed by dissociation of ethene. Theinteraction of a thin film of (CpMoμ-S)₂ S₂ CH₂ with olefins has alsobeen monitored by visible spectroscopy.

Alumina Supported Complexes. The complex (CpMoμ-S)₂ S₂ CH₂ has beenabsorbed on neutral alumina (100 mesh) by the following procedure. A10⁻³ M solution of the complex in CH₂ Cl₂ (25 mL) was added to 5 g ofalumina and the solvent from this slurry was evaporated on a rotaryevaporator. The resulting alumina became light blue, indicating that theblue molybdenum complex had been absorbed.

The solid state absorbed complexes retain their reversible reactivitywith olefins. This has been demonstrated by admitting an atmosphere of agaseous olefin (ethane, propene, or butenes) to a layer of molybdenumtreated alumina. A color change on the surface of the alumina from blueto brown was observed within seconds. The color change is analogous tothat observed for olefin adduct formation in solution. The aluminacontaining the absorbed molybdenum sulfide-olefin adduct was subjectedto thermal desorption analysis. The thermal desorption curves indicatedthat olefins were desorbed over narrow temperature ranges (1°-2°). Forexample, propene was desorbed at 72° C. and trans-2-butene at 83° C. Theidentity of the desorbed species was confirmed by mass spectroscopy. Theabsorption and desorption of olefins was repeated in multiple cycleswithout notable degradation of the absorbed molybdenum complex.

The dried alumina treated with (CpMoμ-S)₂ S₂ CH₂ also reacted with anatmosphere of acetylene as indicated by a color change on the aluminasurface from blue to brown. The coordinated acetylene was not releasedthermally at temperatures up to ca. 100° C. However, addition ofhydrogen to the alumina surface heated at 70° resulted in a slowconversion of the absorbed molybdenum complex back to the bluederivative (C_(p) Moμ-S)₂ S₂ CH₂. The reaction appears to be analogousto that observed in solution.

We claim:
 1. A method of separating alkenes or alkynes from ahydrocarbon mixture by use of differential binding rates or equilibriumconstants of said alkenes or alkynes to a molybdenum-sulfide dimercomprised of the formula: ##STR30## wherein Cp is selected from thegroup consisting of: --C₅ H₅, --C₅ H₄ CH₃, --C₅ H₄ CO₂ CH₃, --CH₅ H₄ CO₂Na, --C₅ H₄ CH═CH₂, --C₅ (CH₃)₅, or C₅ H₄ CHO, R is selected from thegroup consisting of --C₂ H₄ or --CHR', wherein R' is selected from thegroup consisting of H, --CO₂ Na, --CO₂ CH₃, --C(CH₃)₂ CO₂ Et, --C(CH₃)₂CO₂ Li or --CH(CO₂ CH₃)₂, and R" is selected from the group consistingof --C(CH₃)₃, --CH(CH₃)CO₂ H, or nothing, such method comprised of thesteps:preparing said molybdenum sulfide-dimer; contacting saidhydrocarbon mixture with said molybdenum-sulfide dimer, wherein alkenesor alkynes having an increased affinity to the molybdenum-sulfide dimerrelative to the hydrocarbon mixture may be separated from the remainderof the hydrocarbon mixture; separating the increased affinity alkenes oralkynes from the remainder of the hydrocarbon mixture.
 2. The method ofclaim 1 wherein said hydrocarbon mixture comprises a plurality ofalkenes.
 3. The method of claim 1 wherein said hydrocarbon mixturecomprises isomeric alkenes of the same molecular formula.
 4. The methodof claim 1 wherein said hydrocarbon mixture comprises a plurality ofalkenes and a plurality of alkanes.
 5. The method of claim 1 whereinsaid hydrocarbon mixture comprises a plurality of alkynes and aplurality of alkanes.
 6. The method of claim 1 wherein said hydrocarbonmixture comprises a plurality of alkynes and a plurality of alkenes. 7.The method of claim 1 wherein said hydrocarbon mixture contains alkynes.8. The method of claim 1 wherein said hydrocarbon mixture contains H₂ S.9. The method of claim 1 wherein said molybdenum-sulfide dimer isattached to a permselective membrane.
 10. The method of claim 9 whereinsaid membrane is an ion-exchange membrane.
 11. The method of claim 9wherein said molybdenum-sulfide dimer is covalently incorporated intothe polymeric matrix of said membrane.
 12. The method of claim 1 whereinsaid molybdenum-sulfide dimer is on the surface of a solid support. 13.The method of claim 1 wherein said molybdenum-sulfide dimer is in anaqueous solution.
 14. The method of claim 13 wherein saidmolybenum-sulfide dimer is water soluble.
 15. A method for removingalkynes from a gaseous hydrocarbon feed stream by use of differentialbinding rates or equilibrium constants of such compounds to amolybdenum-sulfide dimer comprised of the formula: ##STR31## wherein Cpis selected from the group consisting of: --C₅ H₅, --C₅ H₄ CH₃, --C₅ H₄CO₂ CH₃, --C₅ H₄ CO₂ Na, --C₅ H₄ CH═CH₂, --C₅ (CH₃)₅, or --C₅ H₄ CHO, Ris selected from the group consisting of --C₂ H₄ or --CHR', wherein R'is selected from the group consisting of H, --CO₂ Na, --CO₂ CH₃,--C(CH₃)₂ CO₂ Et, --C(CH₃)₂ CO₂ Li or --CH(CO₂ CH₃)₂, and R" is selectedfrom the group consisting of --C(CH₃)₃, --CH(CH₃)CO₂ H, or nothing suchmethod comprised of the steps:preparing said molybdenum sulfide-dimer;contacting said hydrocarbon feed stream with said molybdenum-sulfidedimer, wherein alkynes having an increased affinity to themolybdenum-sulfide dimer relative to the hydrocarbon feed stream may beseparated from the remainder of the hydrocarbon feed stream; separatingthe increased affinity alkynes from the remainder of the hydrocarbonfeed stream.
 16. The method of claim 15 further comprised of the step:heating said increased affinity alkynes of said molybdenum-sulfide dimerin the presence of hydrogen to release the alkyne and the molybdenumsulfide dimer.